Disturbance generation in supersonic jets under acoustic excitation

Abstract

Experimental results are presented on the interaction of saw-toothed high-intensity sound waves [sound pressure level (SPL) = 160-170 dB] with an axisymmetrical supersonic air jet. The flow and sound waves were visualized by the direct shadowgraph method using a spark light source with exposure time of 2 X 10 ~7 s. It is shown that disturbance increase increment in a supersonic jet under external acoustic excitation depends on the angle of incidence of the sound wave to the jet boundary. The most intensive increase in jet disturbances occurs at an oblique sound incidence when the sound phase velocity along the boundary approaches the disturbance propagation velocity. For sufficiently intense jet disturbances, a shock wave formation induced by and moving with these disturbances may arise. Sound interaction with a supersonic jet takes place within a small flow zone near the nozzle exit; disturbances already developed are not noticeably affected by the sound intensity of 170 dB reached in the experiment.